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Why are some ammo types written with a decimal ex: .22 .38 .45 and others with millimeters ex: 7mm 9mm 10mm
 

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because in europe they are not smart enough to figure out real measurements so they have to use idiot proof mm.

Really it is mostly American cartridges are all in inche measurements and forigen cartridges are in metric. It really depends on the devloper and or the marketing department.
 

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The creator of a cartridge gets to name it. Those created in Europe were typically named using the metric system. America and Britain, fractions of an inch (.22 is 22/100ths, etc) You will also find OLD names, such as 45-70 that designated caliber of bullet in inch fractions, and the weight of black powder.
 

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The creator of a cartridge gets to name it. Those created in Europe were typically named using the metric system. America and Britain, fractions of an inch (.22 is 22/100ths, etc) You will also find OLD names, such as 45-70 that designated caliber of bullet in inch fractions, and the weight of black powder.
Thus endith the lesson... :D

BTW there are 2.54 cm per inch and 25.4 mm per inch, just in case anyone wants to compare .XX" to XX mm. For example a .50 BMG would be approx 13 mm (.5 x 25.4mm). :cool:
 

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The creator of a cartridge gets to name it. Those created in Europe were typically named using the metric system. America and Britain, fractions of an inch (.22 is 22/100ths, etc) You will also find OLD names, such as 45-70 that designated caliber of bullet in inch fractions, and the weight of black powder.
This could be a huge topic. Many make sense, many don't. A quick example is a .38 is really .357....
C3 pretty much got it there.. The creator of the cartridge gets to name it, even if it doesnt make any sense at all..

The case of the .38 spl is .38 not the bullet. from the days of "Heeled" bullets. ;)
 

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I've never understood why it is a .460 Rowland instead of a .46 Rowland.

Why .500 S&W, but .50 AE?

Why .38 special, but .380 auto?

I don't get why the zero is like the silent-p in pterodactyl.
 

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Thus endith the lesson... :D

BTW there are 2.54 cm per inch and 25.4 mm per inch, just in case anyone wants to compare .XX" to XX mm. For example a .50 BMG would be approx 13 mm (.5 x 25.4mm). :cool:
I believe a 12.7mm is a foreign answer to our .50bmg. Not saying they're exactly equivalent, just close enough that it's what they built as their equivalent...
 

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I believe a 12.7mm is a foreign answer to our .50bmg. Not saying they're exactly equivalent, just close enough that it's what they built as their equivalent...
yeah...doing the math a .50 BMG, half an inch, is exactly 12.7 mm
 

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I've never understood why it is a .460 Rowland instead of a .46 Rowland.

Why .500 S&W, but .50 AE?

Why .38 special, but .380 auto?

I don't get why the zero is like the silent-p in pterodactyl.
Because thats what the guy who invented the cartridge wanted to call it! :p
 

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Oh is it? I thought it was off by a couple hundredths or something.
Not sure if a .50 BMG is exactly 50/100th of an inch or not...it may very well be 48.7575829/100ths :p My point was that accepting a .50 caliber round as being 1/2" will equate to 12.7 mm in metric. Using the same logic a 9mm is approx the same as a .357, (.357 x 25.4) a .40 S&W is approx 10mm (.40 x 25.4), etc. Measurements won't match exactly but will be useful as a point of reference.
 

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Great question, but let me add to the confusion. You can not go into a store in Germany and ask for some 12 gauge shotgun shells. It is like asking for some pistol ammo. Ok...what shell size will be your first question. Some shotguns are made for only a certain size. For example 12/63, 12/70, 12/67 and 12/76. Or, .410 and .410/76. My mossberg can take 12/70 and 12/76. Plus the pellets are measured in mm and weighed in grams. I use Sellier and Bellot 12/76, 8.4 mm, 53 g magnum rounds for self defense. I believe it is a 00 in the States. Boom! Also, NATO measures their rifle cartridges in metric too. Why? Because most the countries are in Europe. US is the only country on the planet that does not use metric system. Check out the .223 thread and let the confusion begin. Why the cluster **** on ammo? Because guns are world wide and inventors have naming rights. They will go by their measuring system too. Some ammo have different names, but it is the same ammo. 9mm parabellum and Luger for example. Or, 9 mm short and .380. Best bet is to check the barrel or slide, which will tell you what to put in the gun. Ok, now for the quiz...
 

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But as Billy Mays would say- "But wait- there's MORE!"

The Europeans measure bore diameter differently than the Americans. We measure groove to groove. THEY measure land to land. OUR 7.62 (NATO) is .308. THEIR 7.62 is 3.11.

sometimes it is a matter of convenience. 9mm Makarov has a bullet larger than 9mm. And the .50 BMG has a bore smaller than .50.....

sometimes a matter of marketing. The .44 magnum is actually about .429. Just does not sound the same- "Since this is a 429 magnum, the most powerful handgun in the world, and would blow your head CLEAN off..."

And as said- sometimes a matter of history. At one time bullets were "heel seated". The case grabbed just the back edge of the bullet- like a .22 LR. Cases were same diameter of the bullet. Then we changed to an inside loaded bullet- case now will have larger diameter than bullet. .22 Magnum has larger case diameter than .22 LR.

The history of cartridges is itself a complex field of study- but a lot of fun. Try looking up the .307 Schneelock Triangular. No, not making that up.
 

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Great question, but let me add to the confusion. You can not go into a store in Germany and ask for some 12 gauge shotgun shells. It is like asking for some pistol ammo. Ok...what shell size will be your first question. Some shotguns are made for only a certain size. For example 12/63, 12/70, 12/67 and 12/76. Or, .410 and .410/76. My mossberg can take 12/70 and 12/76. Plus the pellets are measured in mm and weighed in grams. I use Sellier and Bellot 12/76, 8.4 mm, 53 g magnum rounds for self defense. I believe it is a 00 in the States. Boom! Also, NATO measures their rifle cartridges in metric too. Why? Because most the countries are in Europe. US is the only country on the planet that does not use metric ...
Well it does help when going to the LGS to know if you need 2.75, 3 or 3.5 inch shells.
 

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Well it does help when going to the LGS to know if you need 2.75, 3 or 3.5 inch shells.
Thanks, I did not put the US equivalent in my post. The shells are measured in mm over here. Hence the second number after 12/ in my post. Mossberg exports puts it in mm on their barrels. I can put 8 12/76 shells in my 590, and 9 shells in 12/70. I know it gets more confusing.
 

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Thanks, I did not put the US equivalent in my post. The shells are measured in mm over here. Hence the second number after 12/ in my post. Mossberg exports puts it in mm on their barrels. I can put 8 12/76 shells in my 590, and 9 shells in 12/70. I know it gets more confusing.
I shoot Fiocchi shells when I pheasant hunt, they list both metric and inches on the box and the hull.
 
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